Add DWARF for discriminated unions

n Rust, an enum that carries data in the variants is, essentially, a
discriminated union. Furthermore, the Rust compiler will perform
space optimizations on such enums in some situations. Previously,
DWARF for these constructs was emitted using a hack (a magic field
name); but this approach stopped working when more space optimizations
were added in https://github.com/rust-lang/rust/pull/45225.

This patch changes LLVM to allow discriminated unions to be
represented in DWARF. It adds createDiscriminatedUnionType and
createDiscriminatedMemberType to DIBuilder and then arranges for this
to be emitted using DWARF's DW_TAG_variant_part and DW_TAG_variant.

Note that DWARF requires that a discriminated union be represented as
a structure with a variant part. However, as Rust only needs to emit
pure discriminated unions, this is what I chose to expose on
DIBuilder.

Patch by Tom Tromey!

Differential Revision: https://reviews.llvm.org/D42082

llvm-svn: 324426

1 files changed, 0 insertions, 12 deletions

diff --git a/llvm/lib/BinaryFormat/Dwarf.cpp b/llvm/lib/BinaryFormat/Dwarf.cpp
index 169e50e..bea3df8 100644
--- a/llvm/lib/BinaryFormat/Dwarf.cpp
+++ b/llvm/lib/BinaryFormat/Dwarf.cpp
@@ -393,16 +393,6 @@ StringRef llvm::dwarf::ArrayOrderString(unsigned Order) {
   return StringRef();
 }
 
-StringRef llvm::dwarf::DiscriminantString(unsigned Discriminant) {
-  switch (Discriminant) {
-  case DW_DSC_label:
-    return "DW_DSC_label";
-  case DW_DSC_range:
-    return "DW_DSC_range";
-  }
-  return StringRef();
-}
-
 StringRef llvm::dwarf::LNStandardString(unsigned Standard) {
   switch (Standard) {
   default:
@@ -563,8 +553,6 @@ StringRef llvm::dwarf::AttributeValueString(uint16_t Attr, unsigned Val) {
     return InlineCodeString(Val);
   case DW_AT_ordering:
     return ArrayOrderString(Val);
-  case DW_AT_discr_value:
-    return DiscriminantString(Val);
   }
 
   return StringRef();